In offset printing machines, typically an impression cylinder is mounted on a frame for rotation about a fixed axis and a plate cylinder is mounted for rotation about a fixed axis on said frame with its axis of rotation parallel to the axis of rotation of the impression cylinder and with the periphery of the plate cylinder spaced from that of the impression cylinder. Further, a rubber blanket cylinder is interposed between the impression cylinder and the plate cylinder with its axis of rotation parallel to the axes of rotation of the impression cylinder and the plate cylinder. Further, a mechanism is provided to cause the contact pressure of the rubber blanket cylinder against the plate cylinder and the impression cylinder to be adjusted to suitable values such that the image is uniformly transferred from the plate cylinder onto the rubber blanket cylinder and thence to the impression cylinder, and the printing pressure of the rubber blanket cylinder against the impression cylinder is in conformance to the printing sheet thickness interposed therebetween to provide prints of high resolution. Thus, the adjustment of the plate pressure as well as the printing pressure is a very important factor in the printing technique employed in offset printing.
A variety of plate pressure and printing pressure adjusting mechanisms have been employed in the past. However, the conventional mechanisms which are in use adjust the plate pressure and the printing pressure simultaneously, and therefore, the adjustment of these pressures is intricate, requires considerable time and labor, and it is difficult to set the plate pressure and the print pressure to suitable values.
It is, therefore, a primary object of the present invention to solve the difficulties of conventional plate pressure and printing pressure adjusting mechanisms for an offset printing machine and to provide a plate pressure and printing pressure adjusting mechanism in which the plate pressure and printing pressure may be adjusted separately and in which the operator can readily and quickly adjust the pressures accurately while observing the impression cylinder, the blanket cylinder and the plate cylinder during printing operation.